Antenna system



5 o. M. WOODWARD, JR 3 ANTENNA SYSTEM Filed Feb. 22, 1945 INVENTOR.

aawlzll'amw: V 69 ATTORNEY Patented Dec. 5, 1950 ANTENNA SYSTEM OakleyMi Woo'dwardgfln, Princeton, N. J., as-- signor' toRadio "Corporation of America, a cor poration'of Delaware? Application Februarx gl 1945; S erial;N o 5 'ZQJ Z'I 7 Claims". ff ('Cl. 25033) -This;invention ,relates. to antennasystems candt 5 more particularly? to improved s'upportingnand feed means for; the radiator elementsgthereof. I The -;princi pal bjectof the present invention is to provide an improvedradiator structure incorporatingzthe feed connecti ons in such manner that c the radiator itself acts as a protective cover. for-,the ,connections, so that no energized conductor-w-is exposed to ;the Weather except the radiator i- 2 L, 'rod 5 and engages the tubular member I near its lower end to maintain the parts in alignment.

Thefportion of the rod 5which is surrounded'by thethbe'l is approximately one-quarter wave=- length long at the mean; operating frequency.

The members I and 5 cooperate to act as a quarter wavelength coaxial line, short ch cuited at its upp rtemb theidiscf 3. f'iThis causes a substan' if tiall' winfinitef impedance to appear between the 10 low'er' end of the tube I and'thejrod'j', effectively Anothertobjectis to provide a radiator structure of the described typein which a coaxial feed linea actscas a partial ;.or sole support for the a:

radiator-,

Aiurther qobject-is to provide a structureof theidescribedetype incorporating a coaxial line tIHIISfOT-Hlfliyill the connection between; the feed 5 line ;-and the radiator. I

insulating the radiator ,fromthe' member I.

The radiator. is vImnnected to'a' feed line II at oftheicoaxialltype, and is provided 'withianend 5-1 seal msmamr; .I 5." The insulatori'll'fi ""serves 1m Theserand. other objects will become apparent a to those skilled in the art upon consideration of the ,followingdescription, with reference tothe accompanying drawing, of which Figure, 1 is a sectional elevation of a stub sup-v portedradiator -according to prior art,

prevent the: lentra'nce of ,moisture and'idirt' intothefline vI I andin some casesto retain gas in the'' feeli usys'ten lr Referringgto FigUreZ, the ;rod 5.fis"omitted and ;20 th pi nei'l .,;is extended Within thefradiator '1,

Figure 2 is a-sectional elevationof a line-supportedtradiator in accordance withthe instant;

inventione Figure ,3 is a sectional elevationof a modificawhichfis supported ontheline" II by means of i insulating discs 9 and 17. If The'inn'er' conductor of ,the line 1 I is connected .to the lend "closure. .i'

disc 3 .By.' 1this arrangement, the end of the,"

line H is protected-from weather'by thegradiator' tiongof Figure 2, showing application of the in:-

vention tocan antenna ofv the dipole'ctype,

Figure. 4 is a sectional elevation of a'fu'rther.

modification of thejstructure of Fig'ureZ, and

Figure5 isaschematic diagram of an approxii mateaequivalent circuit. corresponding to the 35.;between thelower-end In of the radiator and] structure of Figure-4.

With the advent of eXtensiveuseof frequencies of v fifty; megacycles and higher for. communication, .,a nd. television picture transmissiom. it has become common ,practiceto employ antennasin, which., ,the individual ,radiator elements have.

cross sectional dimensions which are a. relatively ,1; large vfraction of a wavelength. Such radiators]? aref-requentlytmade in the forin of. a hollowcy lindridalltUbe isupported on a parallellresonant linelsection, withltheinnersurface. of the radiator;

acting as /the outer conductor ofcthesupportin'g;

line.

Referringv to Figure 1, a representative-prior"art; structure includesfa tubularradiator I, closedat,

its hpperendby a disc 3, and supported. by 'a rod 5 which is secured at: its upper endto the, disc 3 c and at its lower endto a conductive member 1. The member 1 maybe a mast, a conductive'scre'en I or reflector; a metal-clad outerflwalljof a build-j I I 'cs h ,antenna'impedance Zout to a valuelzinz, BY

ing or the like. ,A n. insulator; 9 siurrounds the" itself, and the'feed line performs the additional function of supportingvthe' radiator; V ,The'loperatiofi ofthedeviceof Figure 2 is" somewhat-different from that of Figure 1, 'The'" =-.oute r conductor of the feed, line cooperates;

with. the innerrsurface of the radiator" I tofactf as a coaxial line section, connected between the output en d lfi or, the line III and the lower endv I I 0 .of a the. radiator I.. A l Denoting the impedance ground i as Zola, *and thelimped'ance presented ,to the upper .end It of the feed linev I I as Z m,

out+j d P" wherewZc is. the'characteristic impedance of the,

linesection formed by the outside of-the line[ l| and. theinside, of .thedradiator I and 'p.' is the electrieal len'gth of the said line section,

where V is the-lengthof theiline section inwave1ength's'..L It will vbe' apparent that the above-described:v linersection operates as a transformer, converting 3 proper selection of the characteristic impedance Z and the electrical length p, Zm may be made of any desired value for any specific value of Zout. Thus the radiator may be matched to the line II without the use of separate transformers or matching stubs.

In some instances it may be desirable for p to be such that b is in effect greater than I, the length of the radiator I. This condition can be met by filling the entire space between the line I I and the radiator element I with dielectric material. The electrical length is then where k is the dielectric constant of the material. The parameter Z0 is also a function of la, as Well as the ratio of the inside diameter 011 of the radiator I to the outside diameter d2 of the line II. The ratio may be determined independently of the other characteristics of the system by adjustment of the wall thicknesses of the radiator I and the outer conductor of the line II.

The electrical length p may be made less than that corresponding to the radiator length Z by connecting the line to a disc 3 within the radiator I, rather than at the outer end, as illustrated in Figure 3. Figure 3 also shows application of the present invention to a dipole structure, comprising a pair of opposed radiators I supported on their respective feed lines I I extending radially of a mast ID'I. It will be apparent without further illustration that a plurality of such structures can be arranged to form an array, such as a turnstile antenna, and that the arrangement of Figure 2 may be substituted for the radiators of Figure 3 if a greater value of p is required.

Figure 4 shows a further modification in which series reactance may be provided at the feed point It or at the output end of the feed line II, or both. An annular tubular portion I9 is provided within the lower radiator I and is connected thereto by a ring 2I at its upper end. The lower end remains open. The member I9 cooperates with the inner surface of the radiator I to function as a short-circuited coaxial line section of length D. This line section represents a reactance Xe in series with the radiator at the output end of the line transformer formed by the radiator I and the outside of the line II. Referring to Figure 5, the approximate equivalent circuit of the structure of Figure 4 comprises the antenna impedance Za, connected in series with the reactance Xd tc'the output of the line transformer T. The value and sign of the reactance X1 is determined by the length D and the characteristic impedance Z0 of the short-circuited line formed by the member I9.

In similar fashion a reactance Xg may be inserted in series with the input end of the line transformer T by providing an annular conductor 23 at the upper end of th e line I I, short-circuited thereto by a ring 25. The value of Xg is determined by the length g of the member 23, and the ratio of the diameter of the member 23 to that of the outer conductor of the line II.

The invention has been described as an improved radiator structure, wherein a coaxial feed line is arranged to serve the additional function of supporting the radiator. The feed line extends coaxlally within a tubular radiator, and is connected thereto at or near the outer end. The inner surface of the radiator cooperates with the outer surface of the feed line to provide a transformer action which is useful in matching the radiator to the line.

I claim as my invention:

1. An antenna system including at least one radiator including a substantially cylindrical tubular conductive member, a disc connected to and forming a closure within said tubular member and a coaxial line having an inner conductor and an outer sheath extending concentrically into said member and terminating near said disc, the inner conductor only of said line being connected to said disc and a series reactance in said system including an annular conductor between said tubular member and the outer sheath member of said line, said annular conductor being connected to one of said members at one end and free of both members at the other end.

2. An antenna system including at least one radiating element in the form of a conductive tubular member, a conductive disc member arranged transversely of said tubular conductive member and having the periphery thereof electrically connected to said conductive tubular member, a coaxial transmission line comprising an inner conductor and a sheath extending into said conductive tubular member and terminating near said disc member, the inner conductor only being connected to said disc member, and a tubular conductor arranged internally of said conductive tubular member and externally of said sheath, said tubular conductor having one end thereof connected to said tubular conductive member, thereby to interpose series reactance in said system.

3. An antenna system including at least one radiating element in the form of a conductive tubular member, a conductive disc member connected to said tubular conductive member and forming a closure within said conductive tubular member, a coaxial transmission line comprising an inner conductor and a sheath extending into said conductive tubular member and terminating near said disc member, the inner conductor only being connected to said disc member, and a tubular conductor arranged internally of said conductive tubular member and externally of said sheath, said tubular conductor having one end thereof connected to the sheath of said coaxial transmission line, thereby to interpose series reactance in said system.

4. An antenna system including at least one radiating element in the form of a cylindrical tubular conductive member, a conductive disc arranged transversely of said tubular conductive member and having the periphery thereof in conductive relationship with said tubular conductive member, a concentric transmission line comprising inner and outer conductors extending into said tubular member and terminating near said disc, the inner conductor only being connected to said disc, and tubular conductors arranged internally of said tubular member and externally of said outer conductor, one of said tubular conductors having one end thereof connected to said tubular conductive member and the other having one end thereof connected to said outer conductor, thereby to interpose series reactance in said system.

5. An antenna system including at least one radiating element in the form of a cylindrical tubular conductive member, a conductive disc arranged transversely of said tubular conductive member and having the periphery thereof in conductive relationship with said tubular conductive member, a concentric transmission line comprising inner and outer conductors extending into said tubular member and terminating near said disc, the inner conductor only being connected to said disc, and tubular conductors .arranged internally of said tubular member and externally of said outer conductors, one of said tubular conductors being arranged at one end of said tubular conductive member and connected thereto and the other tubular conductor being arranged at the innermost end of and connected to said outer conductor, thereby to interpose series reactance in said system.

6. An antenna system including at least one radiating element in the form of a tubular member of conductive material, a concentric transmission line element comprising an inner conductor and a shielding member extending into and terminating Within said tubular member, the inner conductor only being connected to the interior of said tubular member, and a tubular conductor entirely within said tubular member and coaxially arranged between said members, said tubular conductor having one end thereof connected to one of said members and free of both of said members at the other end, thereby to interpose series reactance in said system.

7. An antenna, system including at least one radiating element in the form of a tubular member of conductive material, a concentric transmission line element comprising an inner conductor and a shielding member extending into and terminating within said tubular member, the inner conductor only being connected to the interior of said tubular member, and a tubular conductor completely contained by said tubular member and coaxially arranged between said members, said tubular conductor having one end thereof connected to one of said members at the end of said tubular conductor remote from the end of said one member and free of both of said members at the other end, thereby to interpose series reactance in said system.

OAKLEY M. WOODWARD, JR.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS 

